Variation in Brown Snake (Storeria dekayi) Morphology and Scalation: Sex, Family, and Microgeographic Differences

Abstract

-Sex, family, and microgeographic variation in body size, head dimensions, tail length, and scalation were assessed from 273 wild-caught brown snakes (Storeria dekayi) from seven island and mainland sites near Lake Erie and from 145 neonates born to 25 wild-caught females. Significant differences between males and females were present both in wild-caught snakes and in neonates, with females exceeding males in snout-vent length and number of ventral scales and males exceeding females in tail length, head dimensions, and number of subcaudal scales. Previous analyses have typically focused on the effect that sex differences might have on adult snakes, e.g, in foraging or reproduction. The presence of sex differences among neonates raises the possibility that these differences may be of ecological and evolutionary significance in younger snakes as well. Significant differences among families were found in neonates for all characters except number of labial scales, and significant heritability (estimated from offspring-dam regression) was found for tail length, head length, and numbers of ventral, subcaudal, and temporal scales. Heritable variation in scalation is well known, but this is the first study to document heritable variation in snake morphology. This result is important because heritable variation is an implicit assumption of hypotheses for the evolution of sex, population, and species differences in morphology. Significant differences among sites were found for adult snout-vent length, head dimensions, number of subcaudal scales, and number of temporal scales. In addition, significant phenotypic correlations (e.g, among head dimensions, between tail length and number of subcaudal scales, between snout-vent length and number of ventral scales) and genetic correlations (e.g, between tail length and number of subcaudal scales, between head length and number of ventral scales) were found between pairs of traits. The presence of these correlations suggests that groups of traits may be influenced by the same genetic or ontogenetic processes and may exhibit patterns of correlated evolution. rnal of Herpetol gy, Vol. 31, No. 3, pp. 335-346, 1997 right 19 7 Society for the Study of Amphibians and Reptiles iation in Brown Snake (Storeria dekayi) Morph logy and Scalation: , Family, and Microgeographic Differences Differences in morphology, behavior, or physiology between sexes, among age classes, or among localities may influence ecological relationships and reflect evolutionary trends. In snakes, sex differences in body size and relative head size may result in reduced diet overlap between males and females (Shine, 1991a; Houston and Shine, 1993) and geographic differences in body size and relative head size may reflect adaptation to local prey characteristics (Forsman and Lindell, 1993). Such hypotheses can be strengthened by an understanding of the genetic and ontogenetic processes giving rise to observed patterns of variation. For example, natural selection will result in sex or geographic differences only if traits show heritable variation. In addition, if multiple traits are genetically or ontogenetically correlated (e.g., if they are influenced by the same genes or by the same ontogenetic processes), then ecological or evolution335 This content downloaded from 157.55.39.4 on Fri, 09 Sep 2016 04:13:43 UTC All use subject to http://about.jstor.org/terms